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The Cardiovascular System: Blood Vessels

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1 The Cardiovascular System: Blood Vessels
19 P A R T B The Cardiovascular System: Blood Vessels

2 Long-Term Autoregulation
Is evoked when short-term autoregulation cannot meet tissue nutrient requirements May evolve over weeks or months to enrich local blood flow

3 Long-Term Autoregulation
Angiogenesis takes place: As the number of vessels to a region increases When existing vessels enlarge When a heart vessel becomes partly occluded Routinely in people in high altitudes, where oxygen content of the air is low

4 Blood Flow: Skeletal Muscles
Resting muscle blood flow is regulated by myogenic and general neural mechanisms in response to oxygen and carbon dioxide levels When muscles become active, hyperemia is directly proportional to greater metabolic activity of the muscle (active or exercise hyperemia) Arterioles in muscles have cholinergic, and alpha () and beta () adrenergic receptors  and  adrenergic receptors bind to epinephrine

5 Blood Flow: Skeletal Muscle Regulation
Muscle blood flow can increase tenfold or more during physical activity as vasodilation occurs Low levels of epinephrine bind to  receptors Cholinergic receptors are occupied

6 Blood Flow: Skeletal Muscle Regulation
Intense exercise or sympathetic nervous system activation results in high levels of epinephrine High levels of epinephrine bind to  receptors and cause vasoconstriction This is a protective response to prevent muscle oxygen demands from exceeding cardiac pumping ability

7 Blood Flow: Brain Blood flow to the brain is constant, as neurons are intolerant of ischemia Metabolic controls – brain tissue is extremely sensitive to declines in pH, and increased carbon dioxide causes marked vasodilation Myogenic controls protect the brain from damaging changes in blood pressure Decreases in MAP cause cerebral vessels to dilate to ensure adequate perfusion Increases in MAP cause cerebral vessels to constrict

8 The brain is vulnerable under extreme systemic pressure changes
Blood Flow: Brain The brain can regulate its own blood flow in certain circumstances, such as ischemia caused by a tumor The brain is vulnerable under extreme systemic pressure changes MAP below 60mm Hg can cause syncope (fainting) MAP above 160 can result in cerebral edema

9 Blood flow through the skin:
Blood Flow: Skin Blood flow through the skin: Supplies nutrients to cells in response to oxygen need Helps maintain body temperature Provides a blood reservoir

10 Blood flow to venous plexuses below the skin surface:
Blood Flow: Skin Blood flow to venous plexuses below the skin surface: Varies from 50 ml/min to 2500 ml/min, depending on body temperature Is controlled by sympathetic nervous system reflexes initiated by temperature receptors and the central nervous system

11 Temperature Regulation
As temperature rises (e.g., heat exposure, fever, vigorous exercise): Hypothalamic signals reduce vasomotor stimulation of the skin vessels Heat radiates from the skin Sweat also causes vasodilation via bradykinin in perspiration Bradykinin stimulates the release of NO As temperature decreases, blood is shunted to deeper, more vital organs

12 Blood flow in the pulmonary circulation is unusual in that:
Blood Flow: Lungs Blood flow in the pulmonary circulation is unusual in that: The pathway is short Arteries/arterioles are more like veins/venules (thin-walled, with large lumens) They have a much lower arterial pressure (24/8 mm Hg versus 120/80 mm Hg)

13 Blood Flow: Lungs The autoregulatory mechanism is exactly opposite of that in most tissues Low oxygen levels cause vasoconstriction; high levels promote vasodilation This allows for proper oxygen loading in the lungs

14 Small vessel coronary circulation is influenced by:
Blood Flow: Heart Small vessel coronary circulation is influenced by: Aortic pressure The pumping activity of the ventricles During ventricular systole: Coronary vessels compress Myocardial blood flow ceases Stored myoglobin supplies sufficient oxygen During ventricular diastole, oxygen and nutrients are carried to the heart

15 During strenuous exercise:
Blood Flow: Heart Under resting conditions, blood flow through the heart may be controlled by a myogenic mechanism During strenuous exercise: Coronary vessels dilate in response to local accumulation of carbon dioxide Blood flow may increase three to four times Blood flow remains constant despite wide variation in coronary perfusion pressure

16 Capillary Exchange of Respiratory Gases and Nutrients
Oxygen, carbon dioxide, nutrients, and metabolic wastes diffuse between the blood and interstitial fluid along concentration gradients Oxygen and nutrients pass from the blood to tissues Carbon dioxide and metabolic wastes pass from tissues to the blood Water-soluble solutes pass through clefts and fenestrations Lipid-soluble molecules diffuse directly through endothelial membranes

17 Capillary Exchange of Respiratory Gases and Nutrients
Figure

18 Capillary Exchange of Respiratory Gases and Nutrients
Figure

19 Capillary Exchange: Fluid Movements
Direction and amount of fluid flow depends upon the difference between: Capillary hydrostatic pressure (HPc) Capillary colloid osmotic pressure (OPc) HPc – pressure of blood against the capillary walls: Tends to force fluids through the capillary walls Is greater at the arterial end of a bed than at the venule end OPc– created by nondiffusible plasma proteins, which draw water toward themselves

20 Net Filtration Pressure (NFP)
NFP – all the forces acting on a capillary bed NFP = (HPc – HPif) – (OPc – OPif) At the arterial end of a bed, hydrostatic forces dominate (fluids flow out)

21 Net Filtration Pressure (NFP)
At the venous end of a bed, osmotic forces dominate (fluids flow in) More fluids enter the tissue beds than return blood, and the excess fluid is returned to the blood via the lymphatic system PLAY InterActive Physiology ®: Autoregulation and Capillary Dynamics, pages 3–37

22 Net Filtration Pressure (NFP)
Figure 19.16

23 Circulatory Shock Circulatory shock – any condition in which blood vessels are inadequately filled and blood cannot circulate normally Results in inadequate blood flow to meet tissue needs

24 Circulatory Shock Three types include:
Hypovolemic shock – results from large-scale blood loss Vascular shock – poor circulation resulting from extreme vasodilation Cardiogenic shock – the heart cannot sustain adequate circulation

25 Figure 19.17

26 The vascular system has two distinct circulations
Circulatory Pathways The vascular system has two distinct circulations Pulmonary circulation – short loop that runs from the heart to the lungs and back to the heart Systemic circulation – routes blood through a long loop to all parts of the body and returns to the heart

27 Differences Between Arteries and Veins
Delivery Blood pumped into single systemic artery – the aorta Blood returns via superior and interior venae cavae and the coronary sinus Location Deep, and protected by tissue Both deep and superficial Pathways Fair, clear, and defined Convergent interconnections Supply/drainage Predictable supply Dural sinuses and hepatic portal circulation

28 Developmental Aspects
The endothelial lining of blood vessels arises from mesodermal cells, which collect in blood islands Blood islands form rudimentary vascular tubes through which the heart pumps blood by the fourth week of development Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs The ductus venosus bypasses the liver The umbilical vein and arteries circulate blood to and from the placenta

29 Developmental Aspects
Blood vessels are trouble-free during youth Vessel formation occurs: As needed to support body growth For wound healing To rebuild vessels lost during menstrual cycles With aging, varicose veins, atherosclerosis, and increased blood pressure may arise

30 Pulmonary Circulation
Figure 19.18b

31 Systemic Circulation Figure 19.19

32 (b) Common carotid arteries Subclavian artery Aortic arch Coronary artery Thoracic aorta Branches of celiac trunk: Renal artery Superficial palmar arch Radial artery Ulnar artery Internal iliac artery Deep palmar arch Left gastric artery Splenic artery Common hepatic artery Internal carotid artery Vertebral artery Brachiocephalic trunk Axillary artery Brachial artery Abdominal aorta Superior mesenteric artery Gonadal artery Common iliac artery External iliac artery Digital arteries Femoral artery Popliteal artery Inferior mesenteric artery Ascending aorta External carotid artery Anterior tibial artery Posterior tibial artery Arcuate artery Figure 19.20b

33 Ophthalmic artery Superficial temporal artery Basilar artery
Maxillary artery Occipital artery Facial artery Vertebral artery Internal carotid artery Lingual artery External carotid artery Superior thyroid artery Common carotid artery Larynx Thyrocervical trunk Thyroid gland (overlying trachea) Costocervical trunk Clavicle (cut) Subclavian artery Brachiocephalic trunk Axillary artery Internal thoracic artery (b) Figure 19.21b

34 Arteries of the Brain Anterior Cerebral arterial circle
(circle of Willis) Frontal lobe • Anterior communicating artery Optic chiasma Middle cerebral artery • Anterior cerebral artery Internal carotid artery • Posterior communicating artery Pituitary gland • Posterior cerebral artery Temporal lobe Basilar artery Pons Occipital lobe Vertebral artery Cerebellum Posterior (c) (d) Figure 19.21c,d

35 Common carotid arteries Vertebral artery Thyrocervical trunk Right subclavian artery Costocervical trunk Suprascapular artery Left subclavian artery Thoracoacromial artery Axillary artery Left axillary artery Subscapular artery Brachiocephalic trunk Posterior circumflex humeral artery Posterior intercostal arteries Anterior circumflex humeral artery Brachial artery Anterior intercostal artery Deep artery of arm Internal thoracic artery Common interosseous artery Descending aorta Radial artery Lateral thoracic artery Ulnar artery Deep palmar arch Superficial palmar arch Digitals (b) Figure 19.22b


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